1. Field of the Invention
The present invention relates to a film comprising a metal foil and a flexible epoxy resin layer covered therewith (hereinafter, referred to as "epoxy resin film covered with a metal foil", or "epoxy resin film"), and a flexible printed wiring board produced therefrom. The flexible printed wiring board according to the present invention can be used in electronic equipment, communications apparatus, household electric articles, office automation machines, motor vehicles, cameras, toys or the like. The epoxy resin film according to the present invention also may be used as a shield for a electromagnetic wave, or as a material for making toys.
2. Description of the Related Art
As a material used for a base film of a resin film covered with a metal foil, especially, a flexible printed wiring board, two kinds of films, i.e., polyimide film and a polyester film, are widely used, although a glass-epoxy base film is sometimes employed.
The polyimide film is very widely used for various applications as the base material of the flexible printed wiring board, due to an excellent heat-resistance against to soldering, but the polyimide film has the disadvantages of hygroscopicity and tearability and a very high cost, and thus the applications thereof are limited.
The polyester film has the problems of a poor heat-resistance and flame-retardance, although the other properties thereof are well balanced, but is relatively inexpensive. Therefore, the polyester film is widely used, when soldering is not required, or the requirement for the flame-retardance is not strict.
The glass-epoxy base film has a good heat-resistance and a low hygroscopicity, but the durability thereof under folding is poor, and therefore, the applications thereof are limited.
As explained above, the materials conventionally used as the base film of the resin film covered with the metal foil, particularly for the flexible printed wiring board, have several disadvantages. Namely, the polyimide film is expensive, easily absorbs moisture, and is easily torn; the polyester film has a poor heat-resistance and flame-retardance; and the glass-epoxy resin film has a poor folding durability.